Swine & U: Remember pseudorabies? Implementing PRV vigilance today

By Diane DeWitte, UMN Extension swine educator
Written for submission to The LAND - as the May 24, 2026, Swine & U column

If you’re a hog producer or, like me, a former 4-H swine exhibitor of a certain age, you recall the blood testing, health certificates, vaccinations and eventual eradication of pseudorabies virus (PRV) just after the turn of the century. PRV was first isolated by a Hungarian veterinarian, Aladar Aujesky, in the early 20th century; they named it Aujesky’s disease, and it settled into swine as its natural host. However, as early as 1813 in the United States, the virus was linked to “mad itch” in cattle.

When pig production got larger in the 1970s, PRV was an important disease, with the emergence of a highly virulent form in Indiana. A 1983 U.S. swine industry survey revealed an 18.8% prevalence of PRV in breeding swine. An attenuated live vaccine was approved for use in 1986. The vaccine was used to manage herds with PRV outbreaks, but in many cases, genetics companies focused on developing PRV-free replacement animals through high health strategies and management techniques.

In 1989, a federal-state eradication initiative was launched; the steps included testing and removal of infected pigs, cleanup, and, in densely affected areas, depopulation of herds. In 2004, PRV eradication was completed, with all 50 states, Puerto Rico and the U.S. Virgin Islands declared pseudorabies-free, a designation of Stage V (Free) Status.

A recent outbreak announcement from USDA APHIS

On April 30, 2026, USDA’s Animal & Plant Health Inspection Service (APHIS) announced the detection of PRV antibodies in a small commercial swine facility in Iowa. The discovery was part of a routine testing program.

From the USDA: “Initial traceback indicates that the five affected boars came from an outdoor facility in Texas. Animals from that herd also tested positive for pseudorabies. APHIS is working with officials in Iowa and Texas to expand traceback efforts and identify any additional potential exposures.”

USDA emphasized that PRV has been eradicated from the U.S. commercial swine herd for 22 years but indicated that PRV is still prevalent in feral swine populations in the U.S., and there is occasional spillover of infection to outdoor production herds where contact with feral swine is possible. APHIS is working closely with the Iowa Department of Agriculture and Land Stewardship and the Texas Animal Health Commission to conduct traceback to better understand the detection and prevent further spread.

Pseudorabies is a contagious viral disease of livestock and other mammals; however, pigs are the only natural hosts. While most mammals can be infected, humans, horses, and birds are considered resistant.

What you need to know about pseudorabies today

Our UMN Veterinary Swine Group recently addressed the latest outbreak in their May 5 edition of UMN Swine News. “The reporting on April 30, 2026, of pigs positive to PRV is a good reminder that we cannot be complacent when it comes to infectious diseases.

"Pseudorabies virus (PRV) causes a devastating clinical picture resembling rabies in young pigs, thus the name. This disease is most severe in piglets, causing high mortality as well as tremors, seizures, paralysis, incoordination and ‘dog-sitting’ signs. As they get older, infected pigs experience respiratory disease with fever, coughing, and pneumonia. In sows, PRV causes abortions and stillbirths and in boars the virus can be shed in semen. PRV transmits primarily by direct contact with secretions of infected pigs but other routes such as exposure to contaminated fomites or aerosols can lead to infection.

"PRV was eradicated from U.S commercial swine in 2004, but it remains prevalent in feral pigs mostly in the southern states. PRV can affect other mammals and notably will kill dogs and cats if they get infected by eating PRV positive carcasses. Finding dead cats or dogs can be the first sign that the virus is present on the farm.

"To keep farms PRV-negative, producers should only bring replacement animals and semen from PRV negative sources, ensure that pigs do not come in contact with feral pigs, and should enforce biosecurity protocols of visitors and employees by using farm dedicated clothing and footwear exclusively, and avoid sharing equipment or materials with other farms.

"Veterinary diagnostic laboratories are well equipped to diagnose PRV via PCR or ELISA tests. PRV does not pose a risk to consumer health or affect the safety of the commercial pork supply. USDA APHIS is currently investigating the current case and asking producers and veterinarians to stay vigilant. For any questions, contact your veterinarian."

Feral swine in Minnesota?

Feral pigs occur in the United States with estimates of more than 6 million animals roaming across 38 states. Typically, they are a mixture of escaped domestic pigs, introduced Eurasian wild boars, and hybrids. They’re known by many names: wild pigs, wild boars, wild hogs and razorbacks. They’re considered an invasive species because of their high reproductive rate, the agricultural damage they can do, and their position as a swine disease host which threatens domestic pigs.

A U.S. map highlights their habitats across southern states; Texas, Louisiana, Mississippi, Alabama, Georgia and Florida are most common. They can be found as far north as Oregon and Pennsylvania. They commonly live in Hawaii, and the current U.S. map shows them in all parts of California.

Fortunately, because they thrive best in warm temperatures, Minnesota isn’t commonly a host for feral pigs. The Minnesota Department of Natural Resources (DNR) monitors reports of wild pig sightings, and in most cases, finds them to be escaped domestic pigs. If an owner is identified, they can be returned to their home pen.

Canadian authorities closely monitor feral pigs to our north. Feral Eurasian boar-domestic pig hybrids have developed cold-weather tolerance and are often found in Alberta, Saskatchewan and Manitoba. U.S. and Canadian authorities work together to prevent feral pig border crossings into our state.

What it means

USDA APHIS is leading the eradication effort in Iowa and Texas, and currently the PRV threat is contained. Pig farmers of every size are encouraged to keep an eye on their pigs’ health. Be familiar with PRV disease symptoms and contact your veterinarian if you see changes or decline in your pigs’ health.

As always, implement meticulous biosecurity practices to keep disease out of your herd. Visit National Pork Board’s Pork Checkoff website to learn more.

The Squeal on Pigs initiative challenges us all to report a loose pig sighting. Checking the Squeal on Pigs website, can help locate a local contact to handle any wandering hogs.

Content collected from USDA APHIS, UMN College of Veterinary Medicine Swine Group, Squeal on Pigs, Swine Health Information Center (SHIC).

Diane DeWitte is a UMN Extension Educator focused on swine, based in the Mankato, Minn. area, and can be contacted at stouf002@umn.edu.